1. Lang, J. Bull. mar. Sci. 21, 952–957 (1971); 23, 260–279 (1973).
2. Francis, L. F. Biol. Bull. 144, 73–92 (1973).
3. Äbel, E. F. Zool. Anz. 153, 259–268 (1954).
4. Bonnin, J. P. Bull. Biol. 98, 225–250 (1964).
5. Hoyle, G. in Simpler Networks and Behavior (ed. Fentress, J. C.) 21–38 (Sinauer, Sunderland, 1976).